Cobb Breeder Management Guide

Growth Phases

Female Bodyweight Target

It is very important to understand the body weight curve in the rearing period and basically it can be divided into 3 phases. The first one is from 0-6 weeks in which part of frame size and uniformity are determined for most of the flock’s life. The second phase is from 6 to 16 weeks of age during which the birds should be maintained under a carefully controlled feeding program designed to prevent them from becoming overweight. The third phase is after 16 weeks when the flock needs to accelerate growth rate to prepare for sexual development and achieve proper uniformity, independent of body weight status at that age.

2.1 Start of Brooding Phase (1-14 Days)
The first 14 days are one of the most important times of a bird’s life. Remember the four basics: Feed, Water, Temperature and Air Quality. The importance of the brooding period cannot be over emphasized. The first 14 days of a chick’s life sets the precedent for good performance. Efforts spent at the start of the brooding phase will be rewarded in the final performance of the flock.


  • Fresh feed and water should be made available to chicks on arrival in the rearing house.
  • Brooders and heaters should be checked regularly to ensure that they are working correctly.
  • Supplemental drinkers are recommended from day old to 7 days of age. Use mini drinkers or chick founts, not open trays. This will help to avoid problems with foot infections. Do not place drinkers directly under brooders.
  • All chick boxes should be placed in the house with the appropriate number of boxes aligned with each brooder prior to releasing chicks. Strive for even chick distribution throughout the brood area. Do not stack full boxes inside the house or place full boxes inside the brooding area.
  • Seven day weights are an excellent overall indicator of how successful brooding management has been. The effects of early stress may not be seen until much later and may negatively affect the subsequent reproductive performance of the flock. The main reason for insufficient early weight gain is low feed consumption. Presentation of food in the form of a good quality, small crumble is necessary to get the proper feed intake in the first week. Insufficient feed amount and/or feeder space will affect feed intake, weights and bird uniformity. It is also important to mention that early protein intake will especially affect four-week weights, flock uniformity, and ultimately egg production.
  • Check chicks two hours after placement. Ensure they are comfortable with the temperature.
  • Crop assessment is a useful tool to judge how effectively chicks have found feed and water. Randomly select 100 chicks and gently palpate the crop 6 to 8 hours following placement. (or the next morning if the delivery is later in the day). The crop should be soft and pliable. If the crop is hard, this is an indication the chicks have not found adequate amounts of water. If the crops are swollen and distended with water, the chicks have not found enough feed. A minimum of 95% of the birds’ crops should be full and pliable upon examination.

Place no more than 30 chick/m2 (.36ft2/bird). Brooders should be operating for 24-48 hours before chicks arrive, maintaining a temperature of 85-90°F (29-32°C) 5 cm (2 in) from the litter at the brooder edge. Observe chicks and adjust for their comfort, but be careful not to over heat. The diagrams below illustrate how to observe chicks and correct for the brooding temperature.


Brooding Temperature

2.2 Maintenance Phase
The main objective in the maintenance phase of the bird’s life is weight and fleshing control. It is important that the birds be handed as often as possible and their fleshing scored throughout this phase. The more birds handled at different ages, the better the condition of the birds will be understood. Bird condition at lighting is critical, and the only way to achieve the desired results (at least 85% of the birds in the proper breast shape for a particular age - see chart below) is with proper weight control throughout the maintenance phase.

Fleshing Scores

Fleshing Conformation for Cobb Females

2.3 Preparation for Lay Phase
This is the phase in the bird’s life when consistent weight gains are needed. The objective is to provide enough fleshing and fat reserves to carry the bird throughout the rest of its life. It is very important to understand the following:
  • Placing correct emphasis on regular feed increases
  • Ensuring correct age and condition at light stimulation
  • Maintaining consistent frame size
  • Building adequate fleshing and fat reserve
  • Preventing stalls or drops in weight gain

Remember it is better to delay light stimulation if you feel the birds are not in the correct condition. The best way to achieve good breeder flock egg production is to develop feed and weight programs that prepare the pullets for a uniform response to light stimulation. The response of the hens to light stimulation is based on the condition and body weight of the bird. It is important not to stimulate the flock if it still contains underweight birds. To determine the average body weight at which to begin light stimulation, refer to the relevant breeder management supplement. Flock uniformity should be a minimum of 70% and the birds should achieve the appropriate breed specific average body weight to ensure the proper response to initial light stimulation. If either the average body weight or uniformity are below the breed specific recommendations, consider a delay in initial light stimulation.

Fat Coverings of Pelvic Bones

2.4 Female Body Weight Gain From 16-20 Weeks
It is essential that the female parent achieves sufficient body weight gain between 16 and 20 weeks of age to maximize peak egg production and maintain post peak persistency.

The female’s body composition at lighting is as important as the bird’s body weight. This means that the hen must have adequate fat reserve and fleshing at this point. Birds normally lay down fleshing quite easily between 16 and 20 weeks of age, however this is not the case with building fat reserve.

In order to build an adequate amount of fat deposition the female must have sufficient weight gains in this critical 16 to 20 week period. A good management tool is to have a 33 to 35 percent increase in female bodyweight during the period from 16 weeks (112 days) of age to 20 weeks (140 days). It is also possible to calculate as a guide the BW increase from 16 weeks to first light stimulation, if the flock is light stimulated later than 140 days. This increase should be between 45%-50%.

As a general conclusion it is evident in the Cobb product lines that first light stimulation is not age but body weight dependent. Uniformity of body weight determines in large part the sexual uniformity of the flock and hence the peak production performance and its persistency over 80% and 70% production.